1. Field of the Invention
The present invention relates generally to servo devices used for radio control (hereinafter referred to as R/C) devices, which remotely control miniatures, such as model helicopters, model aircrafts, model cars, model ships, and others, and unmanned operated industrial machines. Particularly, the present invention relates to an improvement of a servo horn, capable of fine-adjusting a rod for coupling a servo device and an operation unit in an accurate positional relationship.
2. Description of the Prior Art
Radio steering servo motors for miniatures or servo devices for radio control are well known (refer to Japanese Utility Model Publication No. 53-43277 and Japanese Utility Model Publication No. 2-32319). Basically, as shown in FIGS. 9 and 10, the servomotor includes a servo circuit which comprises a gear chain 3 for reducing the rotation of a motor 2 inside a case 1 and transmitting the reduced rotation to the output shaft 4 to which a rotary shaft of a variable resistor 5 is coupled. The operation amount of the motor 2 is accurately controlled in accordance with the operation amount of a transmitter by comparing signals created corresponding to a resistance value of the variable resistor 5 with the rotation angle of the output shaft 4 representing a received signal.
A serration 4a is formed around the end of the output shaft 4 protruded from the case 1. An inner serration 6a formed in the center installation hole of a servo horn 6 is fit to the serration 4a. Thus, the servo horn 6 is fixed at a predetermined angle to the output shaft 4 so as to prevent idle rotation. Then, the servo horn 6 is fixed to the output shaft 4 by means of a screw 7 so as to prevent pulling out.
In general, the servo horn 6 is formed of an injection molded engineering plastic, such as, Delrin and Juracom. Four arms 6b extending crosswise from the mounting center are disposed as shown in FIGS. 9 and 10. Plural mounting holes 6c are formed at predetermined pitches along the length of each arm. As shown in FIGS. 11(a) to 11(i), there are servo horns of various types and sizes having horizontal opposed arms, a disc-shaped arm, a hexangularly-extended arm, and T-shaped arm. Some servo horns have no mounting holes but have notches marking the lengths and angles of mounting holes. Users can select a suitable servo horn according to the application or necessary lever ratio. After an unnecessary portion of a servo horn is cut off with, for example, a nipper, the servo horn may be attached to the servo output shaft. In the linkage rod, one end may be coupled at a suitable position on the servo horn 6 and the other end may be coupled to the operation unit. Thus, linkage adjustment is performed as to a linkage angle or a lever ratio to an object to be controlled.
The mechanical linkage adjustment method described above is generally performed in such a manner that the transmitter/receiver is powered on and the steering stick of the transmitter is in a neutral position so that the output shaft of the servo device halts its rotation in the neutral position.
The adjustment content includes three factors: adjustment of the length of a linkage rod or wire according to the distance between a servo horn and the operation unit to be manipulated, adjustment of an mounting angle of a servo horn to the output shaft to select an optimum angle to the operation unit, and adjustment of a mounting position of a linkage rod or wire to a servo horn to select a lever ratio according to the movable range of the operation unit. A failure of any type of adjustment causes an erroneous operation.
Particularly, model helicopters require high precision linkage adjustment. In helicopters, a swash plate is disposed around the main mast linked between an engine installed in the body and the rotor head disposed above the body. The swash plate transmits the control force for pitch to the main rotor blade, aileron, and elevator via the link mechanism. The linkage method to each operation unit from the servo device depends on types of machines and manufactures because of differences in link members in use, precision errors, or characteristics of an airframe. Accordingly, it was needed to adjust the angle at which the horn is attached to the output shaft of the servo device, or the linkage position to the rod from the center shaft of the horn according to the airframe.
FIG. 12 shows, for example, a linkage to a 3-point supported swash plate in a model helicopter (refer to Japanese Utility Model Publication No. 304996).
Referring to FIG. 12, in the linkage method where the rod 13 links the horn 11 of the servo motor 10 functioning as an elevator servo to the swash plate, the horn is attached to the servo output shaft in such a way that the operation range of the rod 13 due to the turning of the horn 11, namely, the rocking range of the swash plate 12 is symmetric and that the operation center line of the horn 11 90° to the rod 13. When the swash plate 12 tilts because of an error of the constituent member or the center of the mass of the airframe, the mounting angle of the horn 11 or the mounting position of the rod has to be changed suitably to set the arm shaft of the horn 11 to be 90° with respect to the rod 13. In the servo motor where a linkage to the swash plate 12 is performed as shown in FIG. 12 in which the horn 15 having a horizontally opposed arm to the servo motor 10 functions as an aileron servo, two rods 16 are connected to a T-shaped crank 17 and a rod 18 is linked between the crank 17 and the swash plate 12 based on the reservation of the torque transmission force or on an operational response. In this case, the horn 15 with two arms as shown in FIG. 12 or a disc-shaped horn shown in FIG. 11 (referred to FIG. 11(b), FIG. 11(c) and FIG. 11(h)) is used. Linkage is required such that each rod 16 is set to be 90° with respect to the operational center line of the horn.
Referring to FIG. 12, since the size of the crank 17 is nearly the same as the diameter of the entire length of the horn 15 or the disc-shaped horn, two rods 16 are attached diagonally to the horn (or in the direction of 180° with respect to the center axis). When the size of the crank 17 is larger than the length of the horn 15, the crank 17 is linked to one end of the rod 16. For this reason, in order to set the operational center line with respect to the rod 16 to 90°, it is required to suitably change the installation position of the rod 16 to the horn 15.
In model cars with engines, a sole servo device may often operate different two members, such as, a carburetor throttle and a brake device. In this case, it is required to suitably make a linkage adjustment according to the type of car or a choice by a manipulator or according to the degree that an engine responds to the amount of operation. In other words, the servo device requires to adjust a linkage between the horn and the rod according to the type of machine to be mounted.
However, in the conventional servo devices, the degree of freedom of the angle where the horn is attached to the servo depends on the number of teeth formed as a serration structure that stops the rotation of the output shaft 4 and the horn (FIG. 10). For example, when the number of teeth formed on the horn is 25, the servo device can rotate only at intervals of 14.4°. In order to adjust finer degrees, the serration structure has to have a larger number of teeth. However, since the diameter of the output shaft of the servo device is small, the number of teeth is limited to reserve the torque transmission. Furthermore, with the horn having rod connection holes formed in advance, the distance from the center of the horn is defined according to the bore pitch. In the horns with no holes formed in advance (see FIG. 11(c)), the linkage adjustment is made by forming holes in a horn at arbitrary positions. This fabrication work is burden to the user. Moreover, there is a case that a new hole for readjustment cannot be formed close to the hole once formed, and the new hole has to be formed in a fresh servo horn. Accordingly, the manipulators frequently trying the linkage adjustment, particularly, expert manipulators participating in competitions, cannot achieve not always satisfactory adjustment.